Mixed DPI in X11

https://wok.oblomov.eu/tecnologia/mixed-dpi-x11/

by somat • 1 year ago

36 25 1 year ago

wok.oblomov.eu

encom• 1 year ago

I've been running a mixed DPI setup for a long time now, with a 4K display center, and a vertical 1080p display on either side (so 3 displays total).

My conclusion from running this and similar mixed DPI setups over many years is that mixed DPI is extremely poorly tested, if at all, by all vendors. KDE Plasma on Wayland finally pretty much gets it right 98% of the time. X11 wasn't a great experience, regardless of what's technically possible.

Windows has so many annoying issues. Apps are often blurry on the low DPI displays. The mouse cursor has no concept of screen DPI, and treats the entire working area as having the same DPI, so you have to hit the "exits" of the high DPI display just right to land on the low DPI ones. Positioning a window across different displays only scales it correctly on one. There's probably more, but I've been 100% Windows free for a couple of years now.

I wonder how OS X handles it. I don't like that OS, but it sounds like the kind of thing Apple would care about getting right.

looperhacks• 1 year ago

macOS doesn't handle it at all, a window is never visible on multiple screens at the same time.

Low DPI screens are near unusable anyway on macOS without subpixel rendering

jojobas• 1 year ago

Ha, so that's just one issue instead of dozens!

Take that, Apple haters.

the_mitsuhiko5• 1 year ago

macOS doesn't handle it at all, a window is never visible on multiple screens at the same time.

It absolutely is during dragging. macOS is perfectly capable of drawing a window on two screens at the same time, but it doesn't let a window cross two screens while resting which I think is a really good user experience choice.

zamadatix• 1 year ago

macOS (and iOS/iPadOS) is one of the least "technically correct" when it comes to DPI (it uses only the render-at-integer-multiple-and-scale approach) but it does support per display settings pretty well. Everything is also built with the assumptions displays will be high DPI so low DPI screens have crap fonts and whatnot. For windows across multiple displays I'd have to check to see the behavior of but I wouldn't hold up hope it's particularly great. Like you say, Microsoft Windows has one of the most ideal technical implementations (fractional per monitor DPI + it at least attempts to display the window across monitors in a way doesn't bitmap scale) and reached this state many years ago but it means nothing if all the apps aren't also updated to support it (much like this article).

The cursor thing isn't really to do with DPI, it's a general thing with mixed reported display sizes regardless if they have the same DPI. I wish more systems had the option to cross borders at the relative position between monitors rather than the absolute but neither is necessarily more correct and I'm sure many prefer the absolute method.

doublerabbit• 1 year ago

X11 wasn't a great experience, regardless of what's technically possible.

I use FreeBSD as my daily driver and as well I use four screens, 2x4k and 2x1080p.

There are glitches and it's no near perfect but I would highly praise Xorg/X11. I've had no issues in a long time; maybe it's your distro.

jstimpfle4• 1 year ago

Positioning a window across different displays only scales it correctly on one.

Apart from automatic OS-level scaling applied as a post-processing step, which is almost guaranteed to look bad, this one is basically impossible to fix (from a technical standpoint). If you need to move "smoothly" between monitors, get identical monitors.

horsawlarway• 1 year ago

I think this post is one of those "technically correct" but functionally wrong rants.

My experience with multiple monitors at different dpis hits nearly every case of failure he points out.

It's a lot more work to configure.

Apps fail to account for it.

Spanning two monitors results in terrible scaling problems.

Apps that do account for it at start up won't account for it during reposition, so they look fine if they open on the right monitor and terrible if moved to the other.

Getting solid workflows for flexible positioning requires hacks like mentioned at the end for xrandr.

Etc...

So sure, you can do it and it sucks.

That's not really the win I think the author seems to think it is.

jstimpfle4• 1 year ago

"Technically correct" about fundamental limitations of reality but you still hate the truth and it's X11's fault?

I'm not even trying to defend X11, I don't have much love for it. I've done some Xlib programming in the past and I've hated it. I've never used Wayland, and I'm mostly on Windows these days.

But, I don't see how one could make a point that X11 is bad because of poor DPI support.

orangeboats3• 1 year ago

Some of the problems are indeed due to the sheer difficulty to implement proper high DPI/mixed DPI support, but some mentioned in the GP are definitely inflicted by the X11 protocol:

Spanning two monitors results in terrible scaling problems.
Apps that do account for it at start up won't account for it during reposition, so they look fine if they open on the right monitor and terrible if moved to the other.

Especially the second point. Applications on Wayland simply get told what scale they should draw on. No need to determine whether they are on the right monitor or the other monitor, yada yada. For those problems, how can you say X11 is not bad, when clearly other protocols have shown the problem is solvable?

the_mitsuhiko5• 1 year ago

I'm not sure where all these "X11 is actually great" posts recently are common from but X11 does not have DPI solved. I encourage you to read this comment [1] to better understand what the actual situation is like.

[1] https://lobste.rs/s/ceylzx/forbidden_secrets_ancient_x11_sca...

baobun2• 1 year ago

The major fundamental issues are there for Wayland too.

Most of the comment is a rant about "X11 proponents". Can we please at least try to keep identity politics out of display servers?

the_mitsuhiko5• 1 year ago

The major fundamental issues are there for Wayland too.

Which fundamental issues does Wayland have with DPI? I'm not aware of there being any fundamental issues with the DPI handling there.

arp242• 1 year ago

Well, I guess I live in some other universe, because X11 really does "just work" for everything I want it to do. I don't really care about X11 vs. Wayland as such, but I have a bunch of WM-related tools that only work on X11 (and is not the sort of thing that can work in xwayland), so...

Aside: I don't know what it is about the Asahi Linux people that they always need to have the most aggressive takes, assuming hostile malicious intent from anyone who doesn't agree with them or doesn't share the same priorities. These people are just absolutely toxic.

baobun2• 1 year ago

TIL the major reason mixed DPI is subpar on X11 is because Gnome is blocking support on Gtk.

Mixed DPI in X11

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